Abstract: (1) A Eucalyptus tetrodonta forest and a Eucalyptus confertiflora woodland were found on different soils in the coastal plains of the Northern Territory. Within the forest and woodland the understorey communities were correlated with slight changes in soil characteristics. (2) Experimental annual early and late dry-season, and biennial early-season fires resulted in little floristic or structural differences after thirteen years of treatment in the forest and twelve years in the woodland. (3) Protection against fire resulted in the development of a dense understorey in both the forest and woodland. The understorey in the forest was dominated by two species of Acacia, and Erythrophleum chlorostachys. In the woodland the understorey was dominated by Acacia holosericea and two broadleaf species. (4) Grass cover was lowest in the forest and highest in the woodland sites burnt late in the dry-season. Grass persisted on the unburnt treatments. An inverse relationship between shrub cover and grass cover was apparent in the woodland but not in the forest, possibly because of the greater abundance of broadleaf species in the woodland. (5) There was no systematic response of individual species to burning. Of the species which showed a significant change in cover, 36% in the forest and 47% in the woodland also showed a significant interaction with experimental block. This interaction between fire-treatment and site was also apparent in the different responses to treatments by species which occurred in both the forest and woodland. (6) The results of this experiment differ from those of similar studies in African savannas where rainforest invades protected plots and grass cover is dependent upon frequent burning. (7) It is concluded that the Eucalyptus communities have had a sufficiently long history of dry-season burning for vegetation patterns to be primarily determined by edaphic factors.